1. Field of the Invention
The present invention relates to an RFID (Radio Frequency Identification) tag that contactlessly exchanges information with an external device and a method of manufacturing the RFID tag. As used herein, the term “RFID tag” may be also referred to as the term “wireless IC tag” by those skilled in the art.
2. Description of Related Art
A RFID tag is known, including a base made of plastic or paper and an antenna section arranged on the base and having an antenna for wireless communication, wherein a circuit chip is mounted on the antenna section, as a conventional RFID tag, which contactlessly exchanges information with an external device represented by a Reader/Writer.
FIG. 1 is a view illustrating an exemplary RFID tag.
Part (a) of FIG. 1 depicts a perspective view of an RFID tag 200, and Part (b) of FIG. 1 depicts a cross section of the RFID tag 200 taken along with line A-A of Part (a) of FIG. 1.
The RFID tag 200 includes a base 201a made of a sheet-shaped PET film, an antenna section 201 having a loop antenna 201b arranged on the base 201a, and a circuit chip 202 that is electrically connected to the loop antenna 201b through bumps 202a and fixedly mounted on the base 201 by an adhesive 203.
The circuit chip 202 included in the RFID tag may exchange a variety of information wirelessly with an external device (not shown) through the loop antenna 201b. 
FIG. 2 is a view illustrating an exemplary method of manufacturing the RFID tag 200 shown in FIG. 1.
In step S21, a wafer 204, on which plural circuit chips 202 are formed on the surface, is prepared and then divided into the plural circuit chips 202, the method of which is called Wafer Dicing. Next in step S22, any one of the divided circuit chips 202 is adhered by an adhesion rotation nozzle 601, with a bottom surface of the circuit chip 202 where the bumps 202a are formed facing the adhesion rotation nozzle 601. Then, the adhesion rotation nozzle 601 rotates 180 degrees, with the circuit chip 202 adhered to the adhesion rotation nozzle 601, so that the opposite surface of the bottom surface, i.e., the top surface of the circuit chip 202, is directed upward in step S23. Next, while the top surface of the circuit chip 202 is adhered to a heating pressure head 602, the circuit chip 202 is separated from the adhesion rotation nozzle 601 in step S24. Subsequently, in a step not shown, the heating pressure head 602 is moved over a place of mounting the circuit chip 202, around which the adhesive 203 is applied on the antenna section 201, with the circuit chip 202 adhered to the heating pressure head 602, so that the circuit chip 202 may be positioned over the mounting place of the base 201a included in the antenna section 201. After then, the heating pressure head 602 moves down, so that the circuit chip 202 is positioned on the mounting place of the base 201a in step S25. In step S25, the positioning is precisely performed to ensure the loop antenna 201b contacts the tiny bumps 202a of the circuit chip 202. Then, the heating pressure head 602 heats the adhesive 203 at a temperature required to cure the adhesive 203, pressurizing the circuit chip 202 not to be floated over the adhesive 203 that has not been cured in step S26. The adhesive 203 hardens as the heating and pressurizing continue to be performed during a predetermined period of time, so that the circuit chip 202 becomes adhered to the base 201a, thus competing the RFID tag 200 in step S27.
The RFID tag thus prepared is generally attached to a product for use. For example, the RFID tag may be attached to a product, such as clothes, which may be easily deformed. In this case, there could occur a problem as described below, such as detachment of the circuit chip or disconnection between the antenna and the circuit chip.
FIG. 3 is a view illustrating an example of detachment of the circuit chip or disconnection of the antenna and the circuit chip in the RFID tag 200 shown in FIG. 1.
In a case where the RFID 200 is attached to a product which may be easily deformed, the antenna section 201 may be also easily bent by deforming of the product, since the base 201a included in the antenna section 201 is made of a material that may be easily bent. Although the base 201a is easily bent, the circuit chip 202 is difficult to bend, so that a bending stress may concentrate on a peripheral area of the circuit chip 202. Therefore, the bumps 202a may be separated from the loop antenna 201b, and this leads to detachment of the circuit chip 202 or disconnection between the circuit chip 202 and the loop antenna 201b. 
Conventionally, a technique is known to public, for example, such as the one disclosed in Japanese Patent Application Publication No. H9-30170, where a circuit chip and its peripheral area are covered with a resin to prevent detachment of the circuit chip in a case where the circuit chip is mounted on a substrate made of a material that is easily bent.
FIG. 4 is a view illustrating an example where the circuit chip 202 and its peripheral area included in, for example, the RFID tag 200 shown in FIG. 1, are covered with a resin in order to prevent the detachment of the circuit chip 202.
Referring to FIG. 4, the resin 205 covers the peripheral area of the circuit chip 202 and the top surface of the circuit chip 202 as well as the adhesive 203 extending off the circuit chip 202. By doing so, it is possible to prevent the deformation of the base 201a included in the antenna section 201 from affecting the peripheral area of the circuit chip 202 that is vulnerable to such deformation, thus preventing the detachment of the circuit chip 202 or disconnection between the circuit chip 202 and the loop antenna 201b. 
In the technique where the circuit chip and its peripheral area are covered with a resin shown in FIG. 4, however, it needs to thicken the resin layer more than a predetermined thickness to sufficiently protect the circuit chip. In the above technique for protecting the circuit chip, for example, the thickness of the resin layer should generally range from about 0.5 mm to about 1.0 mm. However, such a thickness of the resin layer counteracts the demand for a thinner RFID tag.